This invention relates to a retainer clip for a brake shoe that helps to maintain proper shoe geometry. Specifically, retainer clips are mounted to each brake shoe to interact with anchor pins for maintaining shoe contact, proper shoe orientation, and to prevent shoe drag when brakes are not applied.
Drum brakes are widely used in vehicle braking systems. In a typical drum brake, two arcuate brake shoe assemblies are located inside a rotating cylindrical brake drum. Each brake shoe assembly includes a backing plate that carries brake lining friction material. A brake actuator moves the brake shoe assemblies toward the rotating cylindrical brake drum such that the brake lining friction material contacts the inner surfaces of the rotating cylindrical brake drum, thus retarding the rotation of the rotating cylindrical brake drum.
The brake shoe assemblies are mounted to a central plate or brake spider. At one end each brake shoe assembly is pivotally supported on an anchor pin. At the opposite end of each brake shoe assembly, the brake actuator (typically a cam) applies an actuation force against the brake shoe assembly causing the brake shoe assemblies to pivot about axes define by the anchor pins. The brake actuator causes the brake shoe assemblies to pivot away from each other toward the rotating cylindrical brake drum. Return springs are used to return the brake shoe assemblies after each brake actuation. The drum brake also includes a pair of retainer springs for each brake shoe assembly mounted on an anchor pin end. The retainer springs maintain the shoe contact and orientation with the anchor pin and prevent the brake shoe assemblies from dragging when the drum brake is not applied.
In some instances, depending on the braking application, the retainer springs lack sufficient strength and fatigue life. In these circumstances, a heavier duty brake including a full web around the anchor pin is required, which increases cost.
Further, the retainer springs are an extension spring type that is designed such that in the installed condition the retainer spring is in a slight extension that results in a sufficient load to retain the weight of the brake shoe assembly relative to the anchor pin. The retainer spring includes a collection of closed coils with either hooks formed on ends of the coils or hook details attached to the ends of the coils.
There are several disadvantages to using an extension spring design. Coil clashing and stress concentrations can lead to early failure. Coil clashing is caused by the closed coil design where coils collide as a result of normal road vibration, which can result in fatigue failure. Another disadvantage is caused by the spring manufacturing process. This process typically includes coiling spring wire over a mandrel, which introduces a tool mark on the retainer spring. The small diameter of the retainer spring and the closed coil design do not permit process enhancements, such as shot peening, resulting in a stress concentration in the already highly stressed inner coil area. Also, crimping hooks onto the ends of the retainer spring introduces additional tool marks that result in stress concentrations.
Thus, it is desirable to have a brake retaining mechanism that does not require extension springs. The brake retaining mechanism should be robust and be able to be used in multiple brake shoe configurations in addition to overcoming the above referenced deficiencies with prior art systems.
The subject invention includes a retainer clip that is used to maintain proper shoe contact and orientation for a cam actuated brake assembly. The retainer clip eliminates the need for retaining springs currently used in the brake assembly to maintain proper shoe geometry. The retainer clip is mounted to a brake shoe and cooperates with a brake shoe anchor pin to consistently achieve the correct orientation.
In a disclosed embodiment, the brake assembly includes a pair of brake shoes having backing plates for supporting brake linings for actuation by a cam against a rotating drum. Each brake shoe has an anchor end and an actuation end. Each brake shoe is pivotally mounted at the anchor end to a brake spider with an anchor pin. When the brakes are applied, the cam acts against the actuation end causing the brake shoes to pivot away from one another about axes defined by the anchor pins.
In the preferred embodiment, the retainer clip is mounted to the backing plate of the brake shoe. The retainer clip includes a base plate with a pair of transversely extending legs that support opposite ends of the anchor pin. The base plate preferably includes a resilient tab portion that grips a portion of the backing plate. The anchor pin includes a cylindrical body having a pair of pin ends of smaller diameter than the cylindrical body extending outwardly from opposing sides of the cylindrical body. The transversely extending legs of the retainer clip preferably have hooked ends for engaging the pin ends. The hooked ends cooperate with the pin ends to maintain proper shoe geometry.
The subject invention provides a brake shoe retainer clip that eliminates the need for retaining springs. The retainer clip provides a more robust design and has increased fatigue life over prior art systems. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.